Fluid Mechanics
Ch-8
Buoyancy
Pressure
Flow
Fluids
• Fluids flow and alter
shape
• Which states of
matter are fluid?
• Liquid
• Gas
• Plasma
Gasses fill and conform to
their container
• Chlorine gas Cl2
Plasma’s conform to
magnetic fields
• At PPPL they are
experimenting on
the fusion of
hydrogen plasma
Density
  = m/V
• “rho” =
mass/volume
• Density of Steam =
0.598 kg/m3
• Density of Mercury =
13.6 x 103 kg/m3
Buoyancy
• FB = Fg (of displaced
fluid)
• = mo g
Archimedes Principle
• Fnet = mfg - mog
Ships are rated as displacing
tons of seawater
Fluid Pressure
• P = F/A
• Force/unit area
• Pounds/in2 (Psi)
• Or N/m2 (Pascals)
4000 N/m2
• 107 Pascal
Fluid Pressure
• P = F/A
• Force/unit area
• PSI (lbs/insquared)
Pressure increases as area
applied decreases
• F1/A1 = F2/A2
Hydraulics at the Dentist
Syringe hydraulic lift
• I raise a 10 N rock
with a hydraulic
piston that is 13 mm
in radius using water
connected to a 1.5
mm radius syringe.
How much force is
necessary for this lift
to raise the rock?
Pressure as a Function of
Depth
• P = Po + gh
Submarine Ballast Tanks
• The density of the
whole device is
adjusted by
releasing
compressed air
WWIII Submarine section
Buoyant force results from
differing pressure at depth
FB=A(Po+gh2)-A(Po+gh1)
FB=g(h2-h1)A
FB=gV
FB=mfg That’s Archimedes
Principle
The Coanda Effect
• Fluid adheres to
surfaces
• Flowing fluids are
directed by curved
surfaces
Bernouli’s Principle on Air foils
• Air flowing across
and air foil flows
faster across the top
• Pressure is lower of
the air flows faster
• Fnet is upward
Coanda Effect breaks down at
high angles of attack
• The Coanda effect
guides the air flow
along the surface
• The air flow breaks
free and turbulent
flow results
• Stall occurs
Coanda Develops First Jet
engine aircraft, 1910
It crashes,
he loses funding
Lost technology
for 30 years